The invention relates to a method for non-destructively forming a component made of cast material beyond the quasistatic elongation at break.
It is known that casting as a primary forming method affords large degrees of freedom with respect to shaping, functional integration and material selection. Essentially, a change from starting material to raw product is obtained in a single manufacturing step. Nevertheless, it can be favorable to subsequently perform a forming step, for example for producing undercuts or for creating clamped connections. On account of the relatively high brittleness of cast materials, to date there have been no known approaches for further processing cast components by forming.
In general terms, the elongation at break of cast materials does not reach the order of magnitude of, for example, extruded products. Materials predestined for forming are distinguished by elongations at break which generally exceed 20%. By contrast, the elongation at break of cast materials, depending on the alloy and casting method, is often only between 1% (AlSi9Cu3) and 4% (AlSi7Mg). These are in no way sufficient for forming, and cracks or fractures would arise long before a useful degree of forming is achieved. Therefore, materials of this kind have hitherto not been suitable for forming.
One conceivable method for achieving higher elongations at break would be the use of superplastic shaping, which is disclosed in the conference report of the LS-Dyna Users' Forum, Bamberg 2008. However, this presupposes both extremely low forming rates (≈10−4s−1) and strong heating (>0.5*Tm). Here, Tm is to be understood as meaning the melting point of the material on the absolute temperature scale. These boundary conditions require both long process times and a high outlay of energy, which often makes the use of these methods uneconomical.
It is also known, however, that a higher elongation at break usually also accompanies an increasing strain rate in a forming method in metals. However, this effect is all the more pronounced the greater the purity of the materials, and decreases greatly in the case of alloys [Lindholm, U.S. Journal of Materials 6, 1971 (1)]. The hydraulic methods used for materials science investigations [Proceedings of the 1st International Conference on High Speed Forming ICHSF, Dortmund, 2004) or even explosive approaches for generating high strain rates are scarcely suitable for non-destructive forming in series production, since these methods cannot be integrated economically into production processes.
It is an object of the invention to use a method which makes it possible to form cast materials at moderate temperatures of below 150° C.